This study is designed to evaluate transmural myocardial blood flow at rest and during exercise in intact awake dogs with chronic left ventricular hypertrophy. Since coronary blood flow occurs predominantly in diastole, studies will be performed in dogs in which left ventricular hypertrophy has been produced by constriction of the ascending aorta (in which diastolic aortic pressure remains at normal or near normal levels), as well as by production of renal hypertension (in which diastolic aortic pressure is elevated). Myocardial perfusion dynamics will be studied when the hypertrophy inducing stress is imposed in puppies (so that myocardial hypertrophy evolves during the period of growth), as compared with adult dogs, to determine whether growth of the coronary vasculature may not keep pace with the increase in muscle mass when hypertrophy occurs in adult animals. The long term goal of this research is to delineate factors which may be responsible for the clinical and pathologic evidence of subendocardial ischemia which is commonly found in patients with chronic left ventricular hypertrophy.